Optical Position Sensing System and Optical Position Sensor Assembly

ABSTRACT

An optical position sensing system includes a bezel surrounding a display, a position sensor assembly, and a processor for calculating touch locations. Prismatic film may be applied to the bezel. Each optical position sensor assembly includes a body. A lens holder holds an illumination window on a first side and a single element aspherical lens on a second side. The lens holder is mounted to a front face of the body such that the lens is aligned with an opening in the body. An optical sensor is mounted to a rear face of the body and aligned with the opening. A radiation source is positioned within the body above the lens holder and behind an illumination window. A light path separator is positioned between the illumination window and the imaging window, so that the radiation path is optically separated from the view path of the optical sensor.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/019,404, entitled “Optical Position Sensor With Miniature Sensor,” which was filed on Jan. 7, 2008.

TECHNICAL FIELD

The present invention relates generally to electronic sensors, and more particularly to optical position sensors, such as those used in connection with touch sensitive screens.

BACKGROUND OF THE INVENTION

Optical position sensing systems, such as those used in connection with computer displays, office machinery, gaming equipment, etc., rely on a combination of line-scan or area image cameras, digital signal processing, front or back illumination and algorithms to determine a point of touch. Many optical position sensing systems use cameras, orientated along the touch screen surface so as to image the bezel. In this way, the system can track the movement of any object close to the surface of the touch screen by detecting variations in illumination emitted by an illumination source, such as an infrared light source.

While cameras generally are more expensive than other types of detector devices that can be used in optical position sensing systems, such as photo-detectors (e.g., photo-diodes or photo-transistors), they allow greater accuracy for touch detection. As known in the art, cameras using both area scan or line scan sensors are typically expensive and too large in the dimensions which are critical to commercially viable small touch screens.

Conventional optical position sensing systems use optical position sensors comprising multiple refractive elements (i.e., multiple element lens systems). Typically, these refractive elements are plastic or glass lenses. Lenses commonly used in optical sensors and other camera devices are typically designed for imaging applications. They are designed to have low image distortion when imaging a plane surface. Ideally, when light is transmitted and/or refracted onto a lens, all the rays of light are converged to a single point, resulting in a clear image. However, in most lens systems light rays are diverted to different points due to lens imperfections and other influences. These influences are commonly called aberrations, and usually result in distorted images.

Conventional camera devices use multi-element lens systems because the use of multiple refractive elements makes it possible to correct and compensate for aberrations and image distortion over a single element lens system, increasing the clarity of the image. However, the use of multiple elements increases the overall size of the camera, especially the depth, and makes it more difficult to converge light rays at a single point. The problem is exacerbated in configurations where space is extremely limited. While distortion may be undesirable for imaging applications, this is not the case for optical position sensing. Thus, conventional position sensing systems do not require the primary benefit of a multi-lens system. Further, the increased size of multi-lens camera systems not only adds unwanted space to the overall system, but it also adds to the expense of manufacturing these systems.

Additionally, when focusing the lens of conventional multi-element lens systems, manufacturers must physically move the lens elements relative to the body and sensor of the camera. Commonly this is done by a threaded lens barrel, and this results in a camera height which is set by the lens diameter. This is a difficult process given the relatively small amount of available space in a position sensing system. Additionally the multi element lenses and the focusing mechanisms are not mechanically robust, and sensitive to vibration. Unlike imaging applications, slight movement in the optical path causes significant position errors, even when no image degradation would result.

In a retroreflective system, the triangle formed between the illumination source, the nearest point of the reflector, and the lens aperture, must subtend an angle less than the observation angle of the retroreflective material. Existing systems use low performance reflective materials such as beaded material, which compromise performance, and large screen sizes, so that the observation angle is large. Other known systems use expensive beam splitting optics, which are extremely susceptible to dust and contaminants blinding the camera. It is an objective of this invention to use high performance reflective material, on small screens, without expensive beam splitting optics, and with advantageous immunity to blinding from dust and other contaminants.

SUMMARY OF THE INVENTION

The present invention provides an optical position sensing system including an improved optical position sensor assembly. The optical position sensing system includes a display, a bezel surrounding the display, at least one position sensor assembly for emitting radiation to cause illumination of the bezel and for generating data signals representing detected variations in said illumination, and a processor for processing the data signals to calculate a location of a touch relative to the display. Reflectors may be mounted to a face of the bezel that is perpendicular to a viewing area of the display. The reflectors may comprise retroreflective material, such as a prismatic film or tape. The at least one optical position sensor assembly may be mounted to the display or to an overlay that is positioned over the display. The optical position sensor assembly may therefore include one or more alignment features for mounting the optical position sensor assembly to a flat surface, such as the display or overlay.

Each optical position sensor assembly includes a body having a front face and a rear face and an opening therethrough. A lens holder is mounted to the body. The lens holder has a first side and a second side. The first side comprises an illumination window and the second side holds a single element aspherical lens, which may have an f-theta characteristic. The lens holder is mounted to the front face of the body such that the lens is aligned with the opening in the body. An optical sensor is mounted to the rear face of the body and is positioned such that it is aligned with the opening. A radiation source is positioned within the body above the lens holder and behind an illumination window. A light path separator is positioned between the illumination window and the imaging window, such that a path of radiation emitted by the radiation source is optically separated from a view path of the optical sensor. The light path separator may be a flexible printed circuit board that drives the radiation source. Alternatively, the light path separator may be an integral subcomponent of the lens holder or other component of the assembly. In some embodiments, the radiation source and the optical sensor are mounted to a flexible printed circuit board.

The inside face of the imaging window may be shaped to form a shallow convex surface. The imaging window may also or alternatively be dyed to pass a wavelength of radiation emitted by the radiation source and to reject other wavelengths of radiation. For example, the imaging window may be dyed with an optical notch dye. An aperture may be located within the body forward of the lens, i.e., between the second side of the lens holder and the lens. Alternatively, the aperture may be located between the lens and the optical sensor. The assembly is such that the lens position is fixed and the focus of the lens is adjusted by changing the position of the optical sensor relative to the body. The optical sensor may be encapsulated with an encapsulant, with the encapsulant shaped to form a lensed surface. The lensed surface may be convex in a long axis of a photodiode area of the optical sensor.

These and other aspects and features of the invention will be described further in the detailed description below in connection with the appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an optical position sensing system, in accordance with certain exemplary embodiments of the present invention.

FIG. 2 is an illustration of an exemplary optical position sensor assembly according to the present invention.

FIG. 3 is an exploded view of the exemplary optical position sensor assembly shown in FIG. 2.

FIG. 4A is an exploded view of an alternative exemplary optical position sensor assembly according to the present invention.

FIG. 4B is an illustration of the alternative exemplary optical position sensor assembly shown in FIG. 4A.

FIG. 5 is an illustration of a front window with additional active optical surface on the inner face.

FIG. 6 is an illustration of an encapsulated optical sensor chip with integral lensed surface.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present invention provides a novel optical position sensor assembly and a position sensing system incorporating that assembly. The optical position sensor assembly of the present invention is a more compact, simple, robust, and cost efficient device than prior art optical sensors. Consequently, it is suited for use in LCD monitors and computers as well as optical position sensing systems used in devices such as mobile phones, PDAs, bar code scanners, gaming equipment, and other portable computing devices for which minimal device thickness is a priority.

Reference will now be made in detail to various and alternative exemplary embodiments and to the accompanying drawings, with like numerals representing substantially identical structural elements. Each example is provided by way of explanation only, and not as a limitation of the scope of invention. It will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope or spirit of the present disclosure and the appended claims. For instance, features illustrated or described as part of one embodiment of the invention may be used in connections with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure includes any and all modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 is an illustration of an exemplary optical position sensing system 100, sometimes referred to hereinafter as a touch screen system. As used herein, the terms “optical position sensing system” or “touch screen system” are meant to refer to a display 110 and the hardware and/or software components that provide position sensing or touch detection functionality. The exemplary touch screen system 100 includes a display 110 having one or more optical position sensing assembly 130 and interfaced to a computing device 150, which executes software and/or firmware for detecting a touch point (i.e., sensing the position of a pointer) on or near the display 110. The touch screen system thus enables a user to view and interact with visual output presented on the display 110. Those skilled in the art will also appreciate that some optical position sensing systems do not necessarily require a user to touch the display screen in order to interact with it. Accordingly, use of the term “touch” herein is intended to refer generally to an interaction between a pointer and a display screen and not specifically to contact between the pointer and the display screen.

Optical touch screen systems, like the one illustrated in FIG. 1, rely on a combination of electromagnetic radiation, reflectors (or other light guides), optical sensors, digital signal processing, and algorithms to determine the position of a pointer within a viewing area. For example, as shown in FIG. 1A, a bezel 105 borders the viewing area of the display 110. Optical position sensing assemblies 130 are positioned in two or more corners of the display 110. Each optical position sensing assembly 130 can include an electromagnetic radiation source, such as an LED, and an optical sensor, such as a line scan or area scan camera, as will be further described with reference to FIG. 3.

The electromagnetic radiation 140 is guided throughout the viewing area by reflectors 107 applied to the bezel 105 and/or by refractors or other suitable light guide means. The electromagnetic radiation 140 thus “illuminates” the viewing area of the display 110. A pointer or other object placed within the viewing area disturbs the illumination and creates a shadow effect that can be detected by the optical sensors. The position of the shadow, which corresponds to a touch point, can be determined through signal processing and software algorithms, as is well known in the art.

In certain embodiments of the invention, the reflectors 107 comprise retroreflective material, such as film, tape or paint. A common retroreflective material is a “glass bead” film, which has a surface formed by a layer of tiny transparent spheres (i.e., glass beads). Another common retroreflective material is “prismatic” film, which includes an embedded layer of metallized triangular cube corner elements. In each of these forms of retroreflective film, incident electromagnetic radiation waves or beams (i.e. the light beams that enters the film) are reflected back toward the radiation source generally along a line that is parallel to the incident wave or beam. The return pattern (sometimes called “recursive signal”) of a prismatic film is generally less diffuse than that of a glass bead film. As a result, prismatic films have higher reflectivity and are therefore generally more desirable for use as reflectors 107 in some embodiments of the invention. In other embodiments, the reflectors 107 may be any type of recursive or diffusive reflecting material or may be replaced by refractive materials.

The optical position sensing assemblies 130 thus transmit data regarding variations in the electromagnetic radiation 140 to a computing device 150 (or signal processor) that executes software and/or firmware for processing said data and calculating the location of a touch relative to the display 110. The computing device 150 may be any type of processor-driven device, such as a personal computer, a laptop computer, a handheld computer, a personal digital assistant (PDA), a digital and/or cellular telephone, a pager, a video game device, touch screen controller, digital signal processor, etc. These and other types of processor-driven devices will be apparent to those of skill in the art. As used in this discussion, the term “processor” can refer to any type of programmable logic device, including a microprocessor or any other type of similar device.

As shown in FIG. 1B, the optical position sensing assemblies 130 may be mounted to a glass or plastic (or other transparent material) overlay 112 that is positioned over the display 110. In other embodiments, however, the optical position sensing assemblies 130 may be mounted to the surface of the display 110 itself. The electromagnetic radiation sources emit electromagnetic radiation 140, such as ultraviolet, visible or infrared light, into the viewing area of the display 110.

FIG. 2 is an illustration of an exemplary optical position sensor assembly 130 of the present invention. The optical position sensor assembly 130 includes a body 220, which provides outer covering and protection to the various other components of the assembly. Body 220 may be constructed of a plastic or thermoplastic material (e.g., acrylic, Plexiglass, polycarbonate, etc.). In certain embodiments of the present invention, the entire assembly is made waterproof by joining the components with appropriate adhesives and sealants. Body 220 may also be constructed of other materials, as will be apparent to those skilled in the art.

Body 220 includes an alignment face 221 on a lateral side. Alignment face 221 allows body 220 to be placed on a flat surface, such as the surface of the display 110 or an overlay 112. Body 220 may further include alignment and locating features such as flanges 222 positioned proximate to alignment face 221 to the optical position sensor assembly 130 to align the yaw axis and x, y position of the optical position sensor assembly 130 with the edge of the display 110 or overlay 112. The optical position sensor assembly 130 includes a imaging window 250, an illuminator window 262, and light path separator 261, each of which will be described with reference to FIG. 3.

FIG. 3 is an exploded view of the exemplary optical position sensor assembly 130. As shown, an optical sensor 310 is attached to the rear of the body 220 and is aligned behind an opening 323 within the body 220. The optical sensor 310 can be based on complementary metal oxide semiconductor (CMOS), charge coupled device (CCD), or charge injection device (CID) technologies, or any other sensors capable of detecting changes in electromagnetic radiation. Optical sensor 310 may be connected to the computing device 150 a flexible printed circuit board 370 or other suitable connector.

Positioned on each side of the opening 323 of the body 220 is a guide stud 325. Each guide stud 325 aligns with a guide hole 327 on an aperture plate 340. The aperture plate 340, which include the aperture 342, and a lens 330 fit into the back side of the imaging window 250 and may be configured to “snap” into or be otherwise secured into place. The imaging window 250, with the attached aperture plate 340 and lens 330, fits into the body 220 such that each guide stud 325 fits into the corresponding guide hole 327. The guide studs 325 and guide holes 327 ensure that the aperture 342 is substantially centered over the opening 323 (and thus the pixel array of the optical sensor 310). Due to the fixed position of the lens 330, focus may be adjusted by adjusting the position of optical sensor 310. In other words, adjusting the position of optical sensor 310 changes the convergence point of the light refracted through the lens 330 onto the optical sensor 310, thus changing the relative focus of lens 330.

The lens 330 is preferably a single element aspherical lens, with an f-theta characteristic, which can be constructed from transparent plastic material or glass. The single element lens results in reduced internal reflections without resorting to anti reflection coatings and improved accuracy and mechanical stability compared to known multi-element glass lens solutions. The f-theta lens characteristic is desirable in optical position sensing, as it results in a basically linear correspondence between pixel number and angle of refraction. As optical position sensors triangulate using the refraction angle, this results in a smooth low order linearizing function, compared to that from a distortion compensated multi-element design. The assembly illustrated in FIG. 3 results in front-aperture configuration (i.e., the aperture 341 is forward of the lens 330). In other embodiments, lens 330 may be positioned inside a lens holder or other structure.

In still further embodiments, the imaging window 250 may be specifically shaped to function as an active optical surface, thereby enhancing the performance of the lens 330 without increasing complexity of the optical position sensor assembly 130, and without increasing internal reflections. In particular, the inside face of the imaging window 250 can be shaped to form a shallow convex surface, such as illustrated in FIG. 5. FIG. 5A is a front view of the imaging window 250, FIG. 5B is a rear view of the imaging window 250 (i.e., shown proximate to the aperture 342) and FIG. 5C is a top view of the of the imaging window 250. An example of a convex surface 501 can be seen in FIGS. 5B and 5C. As shown in FIG. 5A, no additional optical faces are added and the front surface of the imaging window 250 remains flat and easy to clean. Shaping the imaging window 250 in this or a similar manner allows a significant improvement in spot size of the entire optical system, while allowing the non-optical components of the assembly to remain unchanged.

In other embodiments, particularly those used for very small screens, the aperture 342 may be positioned behind the lens 330. For example, the aperture 342 may be formed as a feature of the body 220 or other component of the assembly 130.

In some cases, the die of the optical sensor 310 may be encapsulated and the encapsulant will result in an unavoidable optical surface. Rather that being plane as is known in the art, this surface can be employed to help correct one or more aberrations of the total optical system. For example, FIG. 6A shows an illustration of an encapsulated optical sensor chip 310 with the encapsulant 603 forming an integral lensed surface, in accordance with embodiments of the present invention. The sensor encapsulant 603 is the only surface placed to improve the telecentricity of the optical system. When infrared radiation is used, commonly in the 850-950 nm range, the light is able to penetrate to a much greater depth in the photodiodes of the optical sensor 310 before being absorbed, compared to a visible light sensor. When a ray bundle 606 enters the optical sensor 310 at an oblique angle, as it does near the edges with a single element lens 330, the lensed surface formed by the encapsulant 603 results in some photoelectrons being produced in the adjacent pixel rather than the pixel through which the light entered. The effect is to reduce contrast.

By forming the encapsulate 603 above the optical sensor 310 to be convex in the long axis of the photodiode area 602, the ray bundle 606 is deflected so that its mean is telecentric at the sensor surface, thus enhancing the contrast. As a secondary effect, the increased Fresnel loss at the edges contributes to equalizing the signal at the edges. In some optical sensors 310, it may be difficult or impossible be able to get the ray bundle 606 perfectly telecentric with acceptable Fresnel loss, and a compromise can be used. For example, as shown in FIG. 6A, the encapsulate 603 may be formed into a lens geometry that reduces the entry angle of the ray bundles 606 at the edge of the photodiode area 602. By shaping the encapsulate 603 such that the angle of the ray bundle 606 is reduced from 52 degrees (with a flat encapsulate face) to 80 degrees (with an appropriately curved encapsulate edge face), the Fresnel loss can be reduced from approximately 64% to less than about 20% (assuming a ray bundle angle of 90 degrees is sought).

The lens formed by the encapsulate 603 can be curved in two axes. However as the light path in an optical position sensing system 100 is typically less than 5 degrees in height, and the photodiode area 602 of a typical optical sensor 310 is narrow, the encapsulate 603 may be formed as a simple singly-curved acircular cylindrical lens to achieve the same results. This cylindrical lens form is advantageous for manufacturing a panel 610 of encapsulated optical sensors 310, as shown in FIG. 6B, in a single operation without critical alignment of the die and optical tooling being required. This encapsulate 603 lens form may be cast directly, or be a separately molded part optically bonded to the optical sensor 310.

Referring again to FIG. 3, the light path separator 261 sits on top of the imaging window 250 and functions to separate the illumination path of the radiation source 363 and the view path of the optical sensor 310. In the illustrated embodiment, the light path separator 261 also functions as the mount for the radiation source 363, which is mounted to a top surface of the light path separator 261. For example, the light path separator 261 may be formed from one or more flexible printed circuit boards, which include circuits for driving the radiation source 363. In other implementations, the light path separator function may be provided by a separate component or may be integrated into another component such as the lens holder 477. The light path separator 261 may also have other compositions and designs, provided that it is highly opaque, as will be apparent to those skilled in the art. Preferably, the light path separator 261 is made of a material that absorbs the appropriate wavelengths of light. Where this is the case, it is desirable that the illumination window 262 is optically integral with the light path separator 261, such as by the use of clear or absorbent adhesive between them.

Illumination window 262 is positioned in front of the radiation source 363. Preferably the radiation source 363 is optically bonded to the illumination window 262 to eliminate Fresnel loss. Any suitable type of radiation source 363 may be used in the inventive optical position sensor assembly 130. For example, the energy source 363 may emit infrared (IR) or near-IR energy. Alternately, the energy source 363 may emit ultra violet or visible light energy (e.g., at one or more frequencies, wavelengths, or spectrums). The energy source 363 may also include one or more separate emission sources (emitters, generators, etc.). For example, the energy source 363 may include one or more light emitting diodes (LEDs).

The imaging window 250 commonly is dyed or coated to pass the

operating wavelength and reject others. In certain embodiments of the invention, especially in embodiments employing the rear aperture design, the lens 330 may have the dye incorporated into it. In embodiments of the invention that use infrared light, the imaging window 250 and/or the lens 330 may be dyed or coated with a material that can filter specific wavelengths of light. Known dyes are long-wavelength pass filters that remove visible light, while passing infrared illumination. This is ideal where 950 nm LEDs are used as a radiation source 363. In other implementations (e.g., when using 850 nm LEDs) it may be desirable to block wavelengths between 900 nm and 1100 nm. An optical notch dye or coating (e.g., centered at 950 nm) can be added to any of the components in the optical paths 150, 330.

The optical sensor 310 may not only be operated at near infrared. In some embodiments, such as those employing optical sensors 310 with small pixels, focus may be enhanced by operation at shorter wavelengths, such as in the range 360-400 nm. In certain embodiments of the invention, the rejection of interference from artificial lighting may be further enhanced by ensuring that the shutter of each optical sensor 310 is synchronized to 2× the mains frequency +/−10%.

FIG. 4 illustrates one of the alternate embodiments of the optical position sensor assembly 130 of the present invention. FIG. 4A provides an exploded view of the alternate optical sensor assembly 130. In this embodiment, the illumination source 363 and optical sensor 310 are mounted to a flexible printed circuit board 475. As shown, the flexible printed circuit board 475 is configured such that the illumination source 363 is above and forward of the optical sensor 310. The flexible printed circuit board 475 is positioned around the opaque body 220 such that the optical sensor 310 is situated behind an opening 323 in the body 220.

A lens holder 477 includes a slot and/or groove on its reverse side for

holding the lens 330. The aperture 342 (not shown) is also integrated into the lens holder 477, either forward of or behind the lens 330. The lens holder 477 has openings on its front side for receiving the imaging window 250 and the illumination window 262. A portion of the lens holder 477 separates the imaging window 250 from the illumination window 262 and thus functions as the light path separator 261. The body 220 includes position guides 480 and an anti-wicking member 482.

An opaque cover 479 covers the optical position sensor assembly 130. The cover 479 may be formed of a flexible substrate and may optionally be sticky, so that it can be used to adhere the optical position sensor assembly 130 to a display 110 or overlay 112. This cover 479 must be opaque to the illumination wavelength. It is preferably absorbent to the illumination wavelength, rather than reflective. The adhesive on the cover 479, makes it optically integral with the top side of the illumination window 262. This and the use of an adhesive on the bottom face of the cover 479 to make it optically integral with the light path separator 261, prevents light piping on the two faces and enhances the directionality of the illumination. The illumination window 262 should be flush or sub-flush of the light path separator 261. This gives the design its high immunity to self blinding by dust on the windows.

FIG. 4B provides a perspective view of the alternate optical sensor assembly 130 (without cover 479 or anti-wicking member 482) and FIG. 4C provides a section view of the alternate optical sensor assembly 130 (without cover 479 or anti-wicking member 482).

Based on the foregoing, it can be seen that the present invention provides

an improved optical position sensing system and optical position sensor assembly. Many other modifications, features and embodiments of the present invention will become evident to those of skill in the art. For example, those skilled in the art will recognize that embodiments of the present invention are useful and applicable to a variety of applications, including, but not limited to, personal computers, office machinery, gaming equipment, and personal handheld devices. Accordingly, it should be understood that the foregoing relates only to certain embodiments of the invention, and are presented by way of example rather than limitation. Numerous changes may be made to the exemplary embodiments described herein without departing from the spirit and scope of the invention as defined by the following claims. 

1. An optical position sensor assembly, comprising: a body having a front face and a rear face and an opening therethrough; a lens holder having a first side and a second side, wherein the first side comprises an imaging window and the second side holds a single element aspherical lens, and wherein the lens holder is mounted to the front face of the body such that the lens is aligned with the opening; an optical sensor mounted to the rear face of the body and positioned such that it is aligned with the opening; a radiation source positioned within the body above the lens holder and behind an illumination window; and a light path separator positioned between the illumination window and the imaging window, such that a path of radiation emitted by the radiation source is optically separated from a view path of the optical sensor.
 2. The optical position sensor assembly of claim 1, wherein an inside face of the imaging window is shaped to form a shallow convex surface
 3. The optical position sensor assembly of claim 1, wherein the imaging window is dyed to pass a wavelength of radiation emitted by the radiation source and to reject other wavelengths of radiation.
 4. The optical position sensor assembly of claim 2, wherein the imaging window is dyed with an optical notch dye.
 5. The optical position sensor assembly of claim 1, wherein the lens has an f-theta characteristic.
 6. The optical position sensor assembly of claim 1, further comprising an aperture between the second side of the lens holder and the lens.
 7. The optical position sensor assembly of claim 1, further comprising an aperture between the lens and the optical sensor.
 8. The optical position sensor assembly of claim 1, wherein the lens position is fixed and the focus of the lens is adjusted by changing the position of the optical sensor relative to the body.
 9. The optical position sensor assembly of claim 1, wherein the light path separator comprises a flexible printed circuit board for driving the radiation source.
 10. The optical position sensor assembly of claim 1, wherein the light path separator is an integral component of the lens holder.
 11. The optical position sensor assembly of claim 1, wherein the radiation source and the optical sensor are mounted to a flexible printed circuit board.
 12. The optical position sensor assembly of claim 1, wherein the body includes one or more alignment features for mounting the optical position sensor assembly to a flat surface.
 13. The optical position sensor assembly of claim 1, wherein the optical sensor is encapsulated with an encapsulant; and wherein the encapsulant is shaped to form a lensed surface.
 14. The optical position sensor assembly of claim 13, wherein the lensed surface is convex in a long axis of a photodiode area of the optical sensor.
 15. An optical position sensing system, comprising: a display; a bezel surrounding the display; at least one optical position sensor assembly for emitting radiation to cause illumination of the bezel and for generating data signals representing detected variations in said illumination; a processor for processing said data signals to calculate a location of a touch relative to the display; and wherein each optical position sensor assembly comprises: a body having a front face and a rear face and an opening therethrough, a lens holder having a first side and a second side, wherein the first side comprises an imaging window and the second side holds a single element aspherical lens, and wherein the lens holder is mounted to the front face of the body such that the lens is aligned with the opening, an optical sensor mounted to the rear face of the body and positioned such that it is aligned with the opening, a radiation source positioned within the body above the lens holder and behind an illumination window, and a light path separator positioned between the illumination window and the imaging window, such that a path of radiation emitted by the radiation source is optically separated from a view path of the optical sensor.
 16. The optical position sensing system of claim 15, further comprising reflectors mounted to a face of the bezel that is perpendicular to a viewing area of the display.
 17. The optical position sensing system of claim 16, wherein the reflectors comprise retroreflective material.
 18. The optical position sensing system of claim 17, wherein the retroreflective material comprises a prismatic film.
 19. The optical position sensing system of claim 15, wherein the at least one optical position sensor assembly is mounted to an overlay that is positioned over the display.
 20. The optical position sensing system of claim 15, wherein an inside face of the imaging window is shaped to form a shallow convex surface
 21. The optical position sensing system of claim 15, wherein the imaging window is dyed to pass a wavelength of radiation emitted by the radiation source and to reject other wavelengths of radiation.
 22. The optical position sensing system of claim 21, wherein the imaging window is dyed with an optical notch dye.
 23. The optical position sensing system of claim 15, wherein the lens has an f-theta characteristic.
 24. The optical position sensing system of claim 15, further comprising an aperture between the second side of the lens holder and the lens.
 25. The optical position sensing system of claim 15, further comprising an aperture between the lens and the optical sensor.
 26. The optical position sensing system of claim 15, wherein the lens position is fixed and the focus of the lens is adjusted by changing the position of the optical sensor relative to the body.
 27. The optical position sensing system of claim 15, wherein the light path separator comprises a flexible printed circuit board for driving the radiation source.
 28. The optical position sensing system of claim 15, wherein the light path separator is an integral component of the lens holder.
 29. The optical position sensing system of claim 15, wherein the radiation source and the optical sensor are mounted to a flexible printed circuit board.
 30. The optical position sensing system of claim 15, wherein the body includes one or more alignment features for mounting the optical position sensor assembly to a flat surface.
 31. The optical position sensing system of claim 15, wherein the optical sensor is encapsulated with an encapsulant; and wherein the encapsulant is shaped to form a lensed surface.
 32. The optical position sensing system of claim 31, wherein the lensed surface is convex in a long axis of a photodiode area of the optical sensor. 